Characteristics of composite materials have meant that composite components are employed in an increasing range of applications from aerospace to automotive parts.
In the aerospace industry, for example, composite materials have been used for a number of years owing to their strength to weight ratio. The term “composite materials” (known also as “composites”) is used to describe materials comprising for example glass fibre or carbon fibres and an epoxy resin (or similar). These are also known as glass reinforced plastic or carbon fibre reinforced composites. The carbon fibre reinforced composite material offers improved properties such as lower weight, improved fatigue/damage resistance, corrosion resistance and negligible thermal expansion.
The use of these materials has increased throughout the aerospace industry predominantly because of the fuel savings which can be achieved over the life of an aircraft by reducing the overall sum weight of the components making up the aircraft. Aerodynamic as well as structural components are formed of composite materials and particularly carbon fibre materials.
A composite component is laid-up using a cloth, tape or the like pre-impregnated with resin to form a stack corresponding to the desired shape of the part to be formed. The stack is then cured either at ambient temperature and pressure or at elevated temperature and pressure in an autoclave to create a hardened component.
A gas turbine engine such as a turbofan may be provided with a containment case for preventing a broken blade of the engine from exiting the engine and damaging the rest of the aircraft. For example, a containment case may be provided around the fan at the front of the turbofan engine. The containment case may be made of composite material such as carbon fibre reinforced composite material and/or Kevlar reinforced composite material. The containment case is in the shape of a generally cylindrical barrel or housing. The containment case needs to be attached to adjacent structural components of the engine and it is therefore desirable for the containment case to include a flange at one or both of the ends of the barrel or housing.
It is convenient to use a machine, such as an automated tape laying (ATL) machine, to lay-up the plies of composite material of the housing of the containment case on a mould or mandrel. It has proved difficult to use a machine to lay-up the plies of the composite material of the flange and to integrate the composite material of the flange with the composite material of the housing, before the housing and the flange are cured. It has proved necessary to manually lay-up the plies of the flange, ply by ply, against an outwardly-projecting annular wall of the mould which extends outward from the main cylindrical mould surface on which the plies of the housing have been machine-laid up. The plies of the flange are hand laid and must be intermeshed with the machine-laid plies of the housing. This tends to produce a flange of inconsistent quality and, in order to compensate for this, a flange which is heavier than it needs to be because it is using an excess of composite material.
As an alternative to using composite, large-diameter containment cases may be machined from a metal such as titanium, so that the flange can be integral with the housing or barrel. However, a titanium fan case is significantly heavier and more expensive than a composite fan case.
The composite containment or fan case described above offers a weight advantage compared with titanium but, in order to have the advantage of the structural integrity resulting from the composite flange being integral with the composite housing of the containment case, there is the disadvantage described above of still having to use manual or hand laying of the flange in order to integrate the flange with the machine-laid housing or barrel.
Generally in relation to composite structures (as well as in relation to the particular example of a containment case), it would be desirable to have a configuration during the laying-up of the composite material which facilitates machine laying of the flange in addition to machine laying of the curved main surface of the composite structure (the housing of the containment case). In this way, all of the laying-up of the composite material could be automated, and it would no longer be necessary to use manual or hand laying. Automating the laying-up of the flange should also produce an improvement in the quality of the flange and the composite structure (the containment case).